The present invention relates to adhesive compositions based on polyurethane including a polyamine suspension. It also relates to a process of preparation and to their use, especially for the adhesive bonding of materials intended for motor vehicles.
In industry, especially the motor vehicle industry, it is often necessary to assemble all kinds of components by adhesive bonding by means of adhesive compositions, in particular heat-curable ones.
Industrial bonding must meet a number of criteria. On the one hand, it must be quick because it is intended to be used on assembly lines at a high rate, not exceeding 5 minutes in most cases. On the other hand, the adhesive bonding must be carried out at moderate temperature, of the order of 120xc2x0 C. to avoid a distortion of the components which, in general, are based on plastics.
Finally, the adhesive bonding ideally requires a xe2x80x9cready-for-usexe2x80x9d adhesive composition (or single-component composition) which, furthermore, is stable for at least 1 month at a temperature lower than 25xc2x0 C.
Heat-curable adhesive compositions are known where adhesive bonding is concerned.
Patent Applications JP-A-071 73243 and EP-A-171 015 describe crosslinkable compositions with delayed reactivity which contain isocyanates and/or urethane prepolymers and amines partially deactivated by means of mono- or polyisocyanates.
JP-A-57 108121 describes a urethane resin intended for the preparation of moulded articles which includes a fine powder of a crosslinking agent such as dodecanediamine.
JP-A-05 032948 proposes a sealing composition based on a polyurethane which has at least one NCO functional group and on a polyamine which has at least two NH2 functional groups, dispersed in a solvent such as liquid paraffin. The solubility of the amine must remain lower than 5 g per 100 g of solution.
It has now been found that the addition of a suspension of polyamine particles of determined size to compositions based on polyurethanes enables their thermal curing to be controlled. The compositions thus obtained exhibit good adhesiveness and storage stability properties.
The subject-matter of the present invention is therefore compositions based on polyurethane prepolymer and on a polyamine suspension, which compositions are characterized in that the free isocyanate functional group content of the polyurethane prepolymer is between 2 and 9% by weight and the polyamine is in the form of particles of mean diameter between 30 and 60 xcexcm.
More particularly, the compositions according to the invention include polyamine particles whose mean diameter is between 40 and 50 xcexcm and, better still, an isocyanate functional group content of between 3 and 8% by weight.
Another subject-matter of the invention relates to a process for the preparation of the said compositions, which consists in reacting at least one polyol and at least one polyisocyanate to form a polyurethane prepolymer which has a free isocyanate functional group content of between 2 and 9% by weight, and mixing the said prepolymer with a suspension of a polyamine whose mean particle diameter is between 30 and 60 xcexcm.
Another subject-matter of the invention relates to the use of the said compositions for the adhesive bonding of materials especially intended for motor vehicles.
The compositions according to the invention are prepared according to the process described in detail as follows:
In a first step at least one polyol is reacted with at least one polyisocyanate to form a prepolymer with isocyanate ends, whose NCO content is between 2 and 9% by weight.
The polyol is generally chosen from polyols which have a functionality higher than or equal to 2, for example polyols of polydiene type, such as polybutadiene and polyisoprene, polyols of polyester type, such as polycaprolactonepolyols, polyols of polyether type, such as polyoxyoxyethylene, polyoxypropylene and polyoxytetramethylene, and mixtures of one or more of these compounds.
Polyols of polyester or polyether type are preferably employed.
The polyisocyanate is generally chosen from aromatic polyisocyanates such as 2,4- or 4,4xe2x80x2-diphenylmethane diisocyanate (MDI) and tolylene diisocyanate (TDI), aliphatic polyisocyanates such as hexamethylene diisocyanate (HMDI), alicyclic polyisocyanates such as isophorone diisocyanate (IPDI), modified polyisocyanates, for example obtained by reaction with trimethylolpropane or water or by cyclization, as well as the mixtures of one or more of these compounds.
Aromatic polyisocyanates and more particularly MDI are preferably employed.
The reaction between the polyol and the polyisocyanate is generally performed at a temperature of between 60 and 110xc2x0 C., preferably 70 and 90xc2x0 C. and for period which varies from 2 to 10 hours, preferably 3 to 5 hours.
The ratio of the number of isocyanate functional groups to the number of hydroxyl functional groups is generally between 1.5 and 3.6 and preferably 2 and 3.
At the end of the reaction a prepolymer is recovered in which the isocyanate functional group content is between 2 and 9% by weight and preferably 3 and 8%.
In a second stage the said prepolymer is mixed with a polyamine suspension in which the mean particle diameter is between 30 and 60 xcexcm and preferably between 40 and 50 xcexcm.
The polyamine is generally chosen from amines containing at least two primary and/or secondary amine functional groups.
The polyamine has a melting point which is advantageously between 50 and 80xc2x0 C. and, better still, between 55 and 70xc2x0 C. 1,12-Dodecanediamine and 4,4xe2x80x2-diaminodiphenylmethane are preferably employed.
The polyamine suspension is generally used in a proportion of 40 to 55% by weight of polyamine in a liquid, and preferably in a proportion of 48 to 52% by weight.
xe2x80x9cLiquidxe2x80x9d is here intended to mean any compound or mixture of compounds that are liquid at a temperature of the order of 25xc2x0 C. and which is not capable of reacting with the free isocyanate functional groups of the abovementioned prepolymer.
The said liquid advantageously has a low ability to solubilize the polyamine.
Examples of such liquids which may be mentioned are the paraffins, polybutadienes, phthalates such as diisooctyl phthalate or di(ethylhexyl) phthalate, and various mixtures based, for example, on isomers of dibenzyltoluene (Jarytherm DBT; Elf Atochem S.A.), on mono- and bis(xylyl)xylene (Jarysol XX; Elf Atochem S.A.), on tetramethylene glycol di-2-hexanoate (Flexol 4GO; Union Carbide) or on phthalates (Santicizer 97 or 128; Monsanto).
At the stage of mixing the prepolymer and the polyamine suspension, the ratio of the number of amine functional groups to the number of isocyanate functional groups is generally between 0.8 and 1.2 and preferably 0.9 and 1.1.
Various additives may be optionally added to the constituents of the abovementioned mixture, such as optionally stearate-treated fillers, for example calcium carbonate, barium sulphate or talc, catalysts, for example tertiary amines such as triethylamine, triethylenediamine or bis(dimethylmorpholino)ethyl ether, metal compounds such as tin or bismuth salts and molecular sieves, preferably 3 or 4 xc3x85.
The mixing of the prepolymer, of the polyamine suspension and optionally of the additives is generally performed at a temperature of between 15 and 30xc2x0 C., preferably 20 and 25xc2x0 C. and for a sufficient period to obtain a homogeneous mixture.
At the end of the mixing stage a composition is recovered which crosslinks in less than 5 minutes at a temperature lower than 120xc2x0 C.
Such a composition retains its adhesive properties in the course of time. It can advantageously be employed for the adhesive bonding of materials based on wood, metal or plastics optionally filled with inorganic and/or organic reinforcing agents. Polyester filled with glass fibres may be mentioned by way of example of such materials.